While it’s a norm to include at least one sidebar for most website designs, I find them more of a distraction than necessity. According to Google Analytics data for my information-intensive websites, page views per visit is 2 or even less. Clicks are extremely likely to happen on in-content links or top menu items rather than links in the sidebar. But I also find contact form submissions are also extremely likely to happen in the sidebar.
Your cases?
I was tempted to do away with them recently, but in the end decided to keep the sidebar for most sites. But it really depends on what you want to have in the sidebar. Let the content tell you if it’s needed or not. Don’t put it there just because the’s the done thing.
From what I remember reading about website usability, people equate the left sidebar with navigation (so will look there, as well as at the top and bottom for nav), and they equate the right sidebar with advertising (so they tend to ignore it)
I don’t like the look of sidebars, so I have only used them on a few special pages. Normally I just use top and bottom nav.
Also sidebars are a real pain-in-the-neck when doing responsive websites…
Agree with all that Greg says, especially with respect to responsive design.